Embodiment
Usually, thickener can mainly be divided into: the function phase, thus it is used to form the engineering properties that conducting film provides electrical property and affects final conducting film to this conducting film; Adhesive, it is used for providing adhesion between described conducting film and the coated substrate of this film; And carrier, it is used for providing machinability to this thickener.In the slug type thickener, use inorganic bond.Raw material used in the thickener can mainly be divided into: be used for providing the metal dust of conductivity, be used for providing the carrier of machinability and conducting film character, and for improvement of thickener to have the additive of required character.Described carrier can be further divided into fluoropolymer resin and organic solvent.Thickener of the present invention comprises aluminium, glass composition, oxide addition and organic carrier.Hereinafter will illustrate in greater detail each component.
A. conductivity aluminium powder
The grain shape of electric conducting material can be spherical, amorphous or flat, or the combination of these shapes.Yet, preferably use the mixture of the different spheric granules of the size of two or three type, to obtain the uniformity of composition.In addition, the mixing ratio as the aluminium powder of electric conducting material can be preferably the following value of being determined by laser diffraction analyzer: D
50The particle that is 1 μ m~3 μ m accounts for 10 % by weight~20 % by weight, D
50The particle that is 5 μ m~9 μ m accounts for 50 % by weight~60 % by weight.If D
50The particle that is 5 μ m~9 μ m accounts for more than 80 % by weight, and then the bending meeting of substrate becomes more obvious behind the sintering solar cell.
B. thickener glass composition
Thickener of the present invention comprises the glass ingredient of 0.1 % by weight~10 % by weight, preferred 0.1 % by weight~2 % by weight.Corresponding glass ingredient comprises Bi
2O
3-ZnO-B
2O
3The type oxide frit, this frit contains Bi
2O
3, ZnO, B
2O
3, Al
2O
3And Na
2CO
3Usually, use the glass composition be of a size of about 0.5 μ m~10 μ m, but suitable be the particle diameter of 1 μ m~3 μ m.
For the electrode of solar battery glass composition, can use based on V
2O
5-B
2O
3, P
2O
5, B
2O
3-ZnO-BaO and Bi
2O
3Glass composition.As follows by the electrode property that uses the glass powder that above-mentioned glass composition makes.At P
2O
5In the situation of class glass, its high-hygroscopicity can the raw material of preparation during glass powder mix and fusion process in and in storage process, have problems, this is can cause change of properties because of moisture absorption, thereby can not keep initial powder properties.In addition, because its proportion is lower, the proportion of electrodes conduct film is also lower when forming electrode, and the conductivity of electrode is deteriorated easily.In addition, B
2O
3-ZnO-BaO class glass is not suitable as the electrode of solar battery glass powder, and this is because its proportion is lower, and its composition almost can not have amorphous state when the lower glass powder of preparation glass transition temperature (Tg).Therefore, the Bi that moisture absorption is lower, proportion (gravity) is higher and can prepare under lower glass transition temperature
2O
3Glass is best suited for electrode of solar battery glass powder of the present invention.According to the suitable mixing ratio of glass composition, can under 350 ℃~500 ℃ glass transition temperature, prepare by different way Bi
2O
3The class glass powder, and the content of its 50 % by weight~70 % by weight is suitable.If B
2O
3Too high levels, then the softening temperature of glass can become higher; If this content is less, then when melting devitrification can appear in glass.Therefore, the B of preferred 10 % by weight~20 % by weight
2O
3ZnO is used for improving resistance and chemical resistance to the loss of glass transparent degree as glass modifier, and crystallization during the content more than 20 % by weight.Al
2O
3That glass network forms agent.The Al of the following content of 15 % by weight
2O
3Be suitable for using, and in situation about using greater than this content, adhesion can be deteriorated because of higher softening temperature.When adding Na with the content more than 5 % by weight
2CO
3The time, it can make the resistance to water of glass and acid resistance die down.Therefore, preferred content is the following Na of 5 % by weight
2CO
3Bi
2O
3Be the steady oxide that can substitute (cope with) Pb, it reduces the softening temperature of glass and improves thermal coefficient of expansion when adding raw material.
C. oxide addition
Oxide addition of the present invention can be selected from: (a) be selected from the metal oxide in the group that is comprised of Al, Si, Zn, Zr, Mg and Ti, (b) be selected from metal in the group that is formed by Al, Si, Zn, Zr, Mg and Ti, (c) in air, can produce the compound of the metal oxide of (b) during sintering, and (d) mixture of above-mentioned substance.
The average grain diameter of metal/metal oxide additive is below the 20 μ m, and is preferably below the 10 μ m.Preferably, this metal/metal oxide additive exists with the content with respect to 0.1 % by weight of whole compositions~2 % by weight.
D. resin
Should carefully select resin so that composition can demonstrate the required character according to application.Because fluoropolymer resin is in the end burning during sintering in the thickener (such as the used for solar batteries thickener) of sintering, therefore but main the selection has the resin of good impressionability, dispersibility and conducting film drying property etc., and usually uses celluosic resin.The preferred resin that uses 0.5 % by weight~10 % by weight, described resin consists of with one or more different materials in the phenolic resin material by being selected from ethyl cellulose, NC Nitroncellulose, hydroxypropyl cellulose, ethylhydroxyethylcellulose, ethoxy hydroxypropyl cellulose, cellulose acetate-butyrate, cellulose-acetate propionate, polyvinyl alcohol, polyvinyl butyral resin, polyester acrylic resin.When to use content with respect to the composition entire contents be resin less than 0.5 % by weight, adhesion and impressionability were not good.When to use content be resin greater than 10 % by weight, sintered density reduced because of a small amount of existence of ash content.
E. solvent
For electrode of solar battery thickener solvent, can use boiling point at one or more solvents more than 150 ℃.Because used organic solvent should satisfy multiple specific indispensable character in the thickener, therefore should select a kind of organic solvent that satisfies respective carrier character.Basically, solvent should have good solvability to the resin that will use.Especially, when silk screen printing, the heat that solvent may produce because of the friction between squeezer and sieve mesh is volatilized, and this moment, machinability may increase relatively poor because of viscosity.Therefore, mainly use the solvent that volatility is lower and boiling point is higher.
Yet, because the character that extremely slow drying can hinder conducting film, so should think over the rear selective solvents such as volatility, boiling point.In addition, for the consideration to safety of workers and Environmental security, preferably select nonpoisonous and tasteless solvent.As common and widely used organic solvent, can use aromatic hydrocarbon solvent, ether solvents, ketone solvent, interior ester solvent, ether alcohol solvent, ester solvent and two ester solvents.Can use the combination of a kind of solvent or two or more solvents.
The preparation of glass composition
Will be based on Bi
2O
3The glass composition of glass powder drops in the platinum crucible, 1200 ℃~1500 ℃ fusings 1 hour, cools off fast with the preparation glass sample subsequently.Use disc mill more than 700rpm, the glass sample that makes thus to be carried out dry grinding, thereby make the glass powder that final average grain diameter is 200 μ m.Subsequently, after to mix 600 gram diameters be 2 millimeters zirconia ball, 200 gram pure water and the described glass powder of 100 grams, use single tank ball mill (mono mill) at 300rpm mixture to be carried out wet lapping 30 minutes, thereby make the glass powder slurry.Subsequently, this slurry dry 12 hours at 100rpm is of a size of the following glass powder of 10 μ m thereby make.
With thus obtained be of a size of below the 10 μ m glass powder and 600 the gram diameters be 0.5 millimeter zirconia ball and 160 the gram pure water mix, and use single tank ball mill at 300rpm this mixture to be carried out wet lapping 30 minutes, below 200rpm dry 12 hours subsequently, thus make the glass powder that final average grain diameter is 1 μ m~2 μ m.
The composition of thus obtained glass powder, glass transition temperature (Tg) and softening point are as shown in following table 1.
[table 1]
The preparation of thickener
The method of making conductive paste feed composition of the present invention is as follows.At first, organic bond and solvent are dropped in the blender together, stirring and dissolving mixt are with the preparation carrier.Subsequently, drop into conductive metal powder, glass composition, ceramic additive and above-mentioned carrier in the planetary-type mixer and stir.
Use three-roll grinder that the thickener through mixing is carried out mechanical mixture and dispersion.Subsequently, by removing by filter impurity such as large-size particles and dust, and use defoamer to remove foam in the thickener.Thus, can make used for solar batteries aluminium paste composition.
The preparation of solar cell
(area is 243cm being coated with antireflecting coating
2And thickness is 180 μ m) silicon wafer on make printed article.
Aluminium thickener in the back of the body surface has used the pre-inclination (pretilt) with 36 μ m, emulsion film and the 200 purpose stainless steel cloths of 5 μ m.Print speed printing speed is adjusted to 200 mm/second~250 mm/second, and with number to be printed be adjusted into make the amount of sprawling be 1.6 the gram ± 0.05 the gram.
For the silver-colored thickener in the front surface, having used finger line (finger line) wide is that 100 μ m and grid live width are 2 millimeters silk screen.As silver-colored thickener, printed the front contact thickener (being SOL-9235H) that derives from Heraeus.Keeping more than 750 ℃ under the condition in 3 seconds at the maximum temperature with wafer simultaneously, the use tape speed is 4 m/mins the above-mentioned front contact thickener of 4 segmentation infrared ray (IR) band oven sintering.
The character of the glass that test program-assessment makes
Use differential scanning calorimetry (DSC:STA449C, Netzsch, Germany) under 10 ℃/minute the rate of heat addition, to measure glass transition temperature (Tg) and softening temperature (Ts).Use dilatometer (DIL402, Netzsch, Germany) under 10 ℃/minute the rate of heat addition, to measure thermal coefficient of expansion.Record thermal coefficient of expansion by the slope in 40 ℃~300 ℃ scopes.
Use particle size analyzer (S3000, Microtrac, the U.S.) to record average grain diameter.
Test program-flexibility
Along with the flat surfaces of the solar cell of laser displacement measuring instrument behind sintering is mobile, record with respect to the maximum displacement value of this flat surfaces and poor (that is, wafer thickness) of least displacement value, and it is expressed as the flexibility of each sample.To measure flexibility with the identical mode that discloses that Korean Patent discloses in 10-2010-0088131 number.
Equation (1) flexibility (mm)=least displacement value (X2)-least displacement value (X1)
Test program-efficient
Under the condition of AM 1.5 sunlights, use solar simulator system (Oriel Instrument Co., model 94063A) that the solar cell that makes according to said process is measured.In following table 2, table 3 and table 4, FF represents to derive from the fill factor, curve factor of I-V curve, and Eff represents electricity conversion.In addition, Voc represents open circuit voltage, and Isc represents short circuit current, and Jsc represents current density, and Pmax represents maximum output, and Rsh represents resistors in parallel, and Rs represents resistors in series.
[table 2]
The glass content of example I in the upper table 2, II, III and Comparative Example I, II, III is to represent with the % by weight with respect to whole paste compositions.
As being the result of the glass composition testing efficiency of 0.1 % by weight, 1 % by weight, 2 % by weight and 4 % by weight with content, table 2 shows that when the glass composition with 1 % by weight added in the example II, its efficient exceeded 2.0% than comparative example II.What can determine in addition, is that crooked character also increases along with glass content increases.When the glass with 4 % by weight added among example I and the Comparative Example I I, the excessive so that battery of flexibility was damaged and can't measures electricity conversion.
Following table 3 shows the effect that oxide addition is mixed with the aluminium thickener, and with the glass content stuck-at-1 % by weight in the example II and test.For oxide, added the Al of 2 % by weight
2O
3, SiO
2, ZnO, ZrO
2, MgO and TiO
2In each check character.
[table 3]
Oxide addition in the upper table 3 and the content of example II are to represent with the % by weight with respect to whole paste compositions.
As above shown in the table 3, compare with the composition that does not contain additive, wherein be added with Al
2O
3, SiO
2, ZnO, ZrO
2, MgO and TiO
2Compositions display go out the crooked effect of significantly improving.Aspect efficient, the most excellent is wherein to be added with Al
2O
3Composition with MgO.
[table 4]
Al in the upper table 4
2O
3With the content of MgO be to represent with the % by weight with respect to whole paste compositions.
With the interpolation content stuck-at-1 % by weight of example II, and with Al
2O
3Be adjusted to 0.1 % by weight~8 % by weight with the interpolation content of MgO.At the Al that adds 1 % by weight
2O
3Situation under, recorded 0.8 millimeter flexibility and 16.2% electricity conversion.What therefore, can determine is with oxide addition Al
2O
3Add in the crown glass additive with MgO, will improve flexibility and improve electricity conversion.
[industrial usability]
The present invention can make because the battery at the crooked caused solar cell of making and occurring during the operation solar cell damages the manufacturing defect that causes and minimize.Thus, the electrical property according to the solar cell of manufacturing of the present invention can be improved.
In addition, the present invention can provide substituting back electrode to hang down the flexure type high performance solar batteries with material to make.